Silicon Surface Modified By Femtosecond Laser Ablation

Femtosecond laser ablation is an important method in processing materials. Si is the most important semiconductor material. With the development of micro electronic technology, man need modify silicon smaller and smaller. We explore a way to induce nanometer structure on silicon surface by femtosecond laser ablation. Interaction between femtosecond laser and condensed matter is an important problem. In this work, we study the mechanism of this process through experiments.In this paper we investigate the silicon surface structured by femtosecond laser ablation(Ti:sapphire laser, wavelength 800nm,100fs). The silicon surface with native oxide is modified by different pulses. We report a kind of fractal-like structure on the surface of Si(100) induced by high repetition rate(1kHz) laser ablation through SEM study. SiOx nano-foam is formed by 500 or more pulses with the scale of less than 10 nanometers. We investigate XPS. It shows the content of oxygen increases when the value of pulses increases. But we only find ridge and pit on the silicon surface blow 500 pulses. When the pulses reach 1000, the surface is almost covered with SiOx nano-foam throughout. We ascribe the forming mechanism of SiOx as ejected silicon ions being oxidized and the coagulating on the surface.We studied Si/SiO2 system formed by oxidation under high temperature. We find micro structure with the width of less than 1 micrometer on Si/SiO2 system by femtosecond laser ablation. Through FT-IR study, we find that the absorption peak near 1100 cm-1and 615 cm-1 is intensified with the increasing of pulses. The absorption peak at 1100 cm-1 promisingly shifts and broadens. The result indicates that the oxidation process is promoted by laser ablation. The depth of the pit is obviously connected with the number of pulses. The appearance of surface is also notably changed with the increasing of pulses.